1. Field of the Invention
The present invention relates generally to an apparatus and a method for estimating a Carrier to Interference and Noise Ratio (CINR) in a wireless communication system. More particularly, the present invention relates to an apparatus and a method for estimating a CINR in a wireless communication system which transmits an orthogonal or quasi-orthogonal signal stream.
2. Description of the Related Art
In a wireless communication system, a base station performs scheduling and determines transmission parameters to send data to terminals. The base station performs these tasks using uplink fast feedback information received from the terminals in its service coverage. With the uplink fast feedback signals received, the base station determines the channel condition of the terminals. Knowing the channel condition of the terminals, the base station transmits data per slot by selecting the terminal having the best channel condition. The base station determines the transmission parameters according to the channel condition information of the terminal to which the data will be sent. Herein, the transmission parameters include a data rate, a coding rate and a modulation order.
When the wireless communication system adopts an Orthogonal Frequency Division Multiple Access (OFDMA) scheme, the terminals send the fast feedback information to a serving base station on a physical channel for sending the uplink fast feedback information. Herein, the physical channel is referred to as a fast feedback channel.
That is, in the time interval for the communications with the serving base station, the terminals periodically report the fast feedback information to the serving base station using the fast feedback channel.
In doing so, the base station controls a power of the uplink channel by estimating a Carrier to Interference and Noise Ratio (CINR) of the fast feedback channel received from the terminals so as to mitigate the inter-cell interference. The base station controls the power of the uplink channel using the CINR of the fast feedback channel as the CINR of the uplink channel. For example, the base station estimates the CINR using extra information relating to codewords and pilots of symbols received from the terminals in the service coverage on the fast feedback channel.
When the CINR estimated by the base station is inaccurate, the operation of power control of the uplink channel is not precisely carried out. As a result, the increased inter-cell interference degrades the link performance and Quality of Service (QoS) requirement is not satisfied.
Therefore, the base station of the wireless communication system requires a method for estimating a reliable CINR of the fast feedback channel.